1. Field of the Invention
The present invention relates to radiography apparatuses for performing computer tomography (CT) reconstruction on a plurality of pieces of image data, and more particularly, to a radiography apparatus for determining a CT reconstruction area on the basis of an X-ray irradiated area of the image data.
2. Description of the Related Art
FIG. 16 schematically illustrates a known technology. CT reconstruction is performed using a plurality of pieces of image data 001 as input image data, and CT images 002, which are tomograms, are acquired. Representative image data 003 is one piece of image data included in the image data 001. A CT reconstruction area 004 is designated by a radiographer.
In order to acquire the CT images 002 from the image data 001, a CT reconstruction area must be determined. The following three procedures are known as the main procedures for determining a CT reconstruction area:    (A) Perform CT reconstruction on the whole image data as a reconstruction area without designating a reconstruction area;    (B) Perform reconstruction using a fixed reconstruction area determined in advance; and    (C) Perform CT reconstruction by using the representative image data 003 from among the plurality of pieces of image data 001 as a scanogram and designating the CT reconstruction area 004 by a radiographer, as described in Japanese Patent Laid-Open No. 2000-316840.
However, according to procedure (A) in which the whole image data is used as a reconstruction area, an increased computation time is necessary for CT reconstruction and a CT image of an area unnecessary for diagnosis is generated. Thus, diagnosis efficiency may be reduced. Also, according to procedure (B) in which a fixed reconstruction area is used, a CT image of an area necessary for diagnosis may not be acquired depending on the influence of the position or shape of a patient. Also, a CT image of an area unnecessary for diagnosis may be generated. Furthermore, according to procedure (C) in which a radiographer designates a reconstruction area, the radiographer must manually perform a troublesome operation. This manual operation reduces the throughput of CT radiography.